1. Field of the Invention
The present invention relates to a synchronous machine control apparatus provided with an electric-power conversion unit for rotation-driving a synchronous machine and particularly to a synchronous machine control apparatus that corrects an error between the true rotor position of a synchronous machine and a rotor position detected by a position detection unit.
2. Description of the Related Art
When in controlling a synchronous machine, there exists an error between the true rotor position of the synchronous machine and a rotor position detected by a position detector (referred to as a rotor position error, hereinafter), the synchronous machine cannot be controlled in such away as to have desired torque. Therefore, this error needs to be detected and corrected.
As an example of synchronous machine control apparatus in which such a problem is solved, a method has been proposed in which under the condition that the load torque is constant, a current command that makes the armature current minimum is searched and the rotor position error is calculated from the searched current command (for example, refer to Patent Document 1).
In addition, a method has been proposed in which there is provided a comparator that compares the U-phase voltage and the W-phase voltage of respective rotor armature windings and makes an output clock signal fall when detecting a point where the U-phase voltage and the W-phase voltage cross each other (the U-phase voltage rises/the W-phase voltage falls) and in which the average value of a predetermined number of position-detector outputs to be obtained each time the output clock signal falls is calculated so that the rotor position error is calculated (for example, refer to Patent Document 2).
[Patent Document 1] Japanese Patent Application Laid-Open No. 2001-8486
[Patent Document 2] Japanese Patent Application Laid-Open No. 2008-278606
However, the synchronous machine control apparatus disclosed in Patent Document 1 has a problem that it takes a long time to search a current command, for calculating a rotor position error, that makes the armature current minimum under the condition that the load torque is constant. The synchronous machine control apparatus disclosed in Patent Document 2 has a problem that for the purpose of calculating a rotor position error, a dedicated circuit is required.